5aSP9. Determining vocal tract shape with small section length given only
a few formants.

Vocal tract shape made up of cylindrical sections of equal length can be
determined given the formant data of vowel sounds; the number of sections
equals twice the number of formants. For an adult male speaker, use of four
formants, results in a large section length of 2.125 cm. If section length of
0.5 cm is desired, 17 formants have to be specified which appears impractical.
A method for obtaining vocal tract shape with small section lengths, given only
a few lower formants (up to fourth or fifth) is presented. For vocal tract of M
sections, only the lower M/2 formants are independent and upper formants are
constrained by the lower formants. This constraint gives unrealistic locations
for the upper formants. One method for predicting the upper formants would be
to use those of a uniform tube of same length as that of the vocal tract. For a
desired section length (say 0.5 cm), the required formants (say, 17) can be
specified by using the given lower formants (say, four) and predicted upper
formants (say, from 5 to 17). Validation of the method using x-ray data and
simulated vocal tract shapes is presented.